1. Field of the Invention
The invention relates to a master unit and to a remote unit for distributing and combining signals of at least one wireless communication network and of at least one digital network. The invention further relates to a multiband transmission system with a master unit of this type and with a remote unit of this type.
2. Description of the Background Art
A multiband transmission system of the above-mentioned type is basically used for distributing and combining signals of at least one wireless communication network and of at least one digital network. The master unit is hereby used for relaying and amplifying signals between a base station and the remote unit. The remote unit is set up for communication with the end user, in particular by means of a mobile terminal. The communication is hereby carried out bi-directionally. This is referred to as a downlink direction with a signal propagation direction from the base station or the master unit to the remote unit or to the end user and an uplink direction in the case of a signal propagation direction from the end user to the master unit or to the base station.
The master unit is radio-connected or cable-connected to the base station and transmits in the downlink direction and respectively receives in the uplink direction signals of different mobile communication standards in different frequency bands, such as GSM, DCS, UMTS, LTE, AWS, PCS, WiMAX, etc. In addition, data or signals of a digital communication network, such as digital video data or audio data, DVD, etc. are exchanged. The respectively received signals are processed in the master unit, in particular amplified, and relayed to a remote unit in the downlink direction or received therefrom in the uplink direction. The signals of the wireless communication network are transmitted to the end user or received therefrom via the remote unit. Likewise, the end user can communicate in a cable-connected manner within the digital network via the remote unit, in particular exchange data between the terminals connected to the network, for example, computers, control devices, televisions etc. or control devices hereby.
A remote unit is provided, for example, for different rooms or floors of a building in order to achieve a locally sufficient signal strength for the end user. A central master unit hereby supplies in particular a plurality of remote units. To separate the two signal propagation directions, generally the two techniques FDD (Frequency Division Duplexing) and TDD (Time Division Duplexing) are known.
In the transmission of signals between the master unit and the remote unit by means of frequency division duplexing, and in particular also with the simultaneous transmission of digital and analog signals, an undesirable intermodulation between the frequency bands used can occur. The signal quality is impaired as a whole hereby. A clean separation of the frequency bands on the receiver side may be no longer possible. These problems have already been discussed, for example, in the IEEE Transactions on Communications, Vol. COM-24, No. 9, September 1976, page 1008 et seq.
From U.S. Pat. No. 7,336,680 82 an architecture is known for a multiband transmission system for transmitting frequency multiplexed signals of different standards according to a point-to-point configuration. For a bi-directional communication between a central unit and an end user frequencies are statistically assigned to the individual frequency channels and a point-to-point connection channel is hereby created. A certain frequency is thereby assigned to the signals with highest priority. The frequencies of the other signals are assigned dynamically. The data of different standards are thus transmitted by corresponding modulation within the assigned frequency bands. The frequencies themselves are not converted.
From U.S. Pat. No. 7,088,921 B1 a system is known for transmitting Ethernet data via a passive optical network in a point-to-multiple point system. Although to avoid collisions in the uplink direction the Ethernet data are modulated with the aid of an FSK modulator to a carrier signal here, the combination of the different uplink data streams takes place only after the electro-optical conversion.
From US 2008/0192855 A1 a system is known for transmitting so-called MIMO signals. MIMO here stands for the abbreviation “multiple input multiple output,” wherein several antennas spatially separated from one another are used to increase the radio transmission rate within a frequency or within a frequency band. In US 2008/0192855 A1 for the separation of the MIMO signals of the same frequency it is provided to separate them from one another by frequency conversion and subsequently to transmit them jointly in a cable-connected manner. In particular one of the MIMO signals is hereby transmitted at the same frequency. The other MIMO signals are frequency-converted suitably accordingly to prevent an intermodulation. To reestablish the original MIMO signals by a frequency shift-back, a reference signal is concomitantly transmitted.
Also from U.S. Pat. No. 5,339,184 a multiband transmission system is known for transmitting a plurality of radio signals of different frequencies. There the frequency bands of all signals of different frequencies are converted to an identical number of non-overlapping frequencies or frequency bands. The signals of the non-overlapping frequency bands are transmitted optically between a master unit and a remote unit. After the transmission in both directions, the frequencies are respectively reconverted again.